System and method for sensing human activity by monitoring impedance

ABSTRACT

A system for sensing human activity by monitoring impedance includes a signal generator for generating an alternating current (AC) signal, the AC signal applied to an object, a reactance altering element coupled to the AC signal, an envelope generator for converting a returned AC signal to a time-varying direct current (DC) signal, and an analog-to-digital converter for determining a defined impedance parameter of the time-varying DC signal, where the defined impedance parameter defines an electromagnetic resonant attribute of the object.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/078,028, filed Apr. 1, 2011 entitled “System and Method forSensing Human Activities by Monitoring Impedance,” which claims benefitof U.S. provisional patent application Ser. No. 61/322,084, filed Apr.8, 2010. Each of the aforementioned related patent applications isherein incorporated by reference in its entirety.

BACKGROUND

Research and development in technologies for sensing human activity isat the forefront of an area known as human computer interaction (HCI).The term HCI refers broadly to any interaction between a computingsystem and a human being, and more particularly, to an interaction inwhich a human being communicates their intention to a computing system.One way a human being can communicate their intention to a computersystem is by having the computer system sense the presence of the humanbeing using a sensor. Examples of such sensors include a proximitysensor and a touch sensor. The desire to sense human activity andcommunicate human intention to a computer system is leading to thedevelopment of new technologies for enabling new types of human-computerinteraction. Designing new interactive experiences is one example of anew type of human-computer interaction that exemplifies the need todevelop new systems and methods for sensing human activity.

There are a number of different sensing methodologies for detecting thepresence and type of human activity and interaction. A sensor is atransducer that converts a physical stimulus, such as light or motion,into a signal that can be measured. The application of the sensordepends on the physical phenomenon sought to be measured, e.g.,resistance is measured in resistive touch panels, light intensity ismeasured in cameras and photo sensors, the direction and intensity of amagnetic field is measured in proximity sensors, acceleration is used tomeasure motion, and the amount of electrical charge can be used tomeasure a response of a multi-touch capacitive input device.

When implemented as part of a user interface, one or more sensors can belocated in an input device associated with the user interface. Thesensor or sensors can be worn by the user or can be embedded intoobjects and the environment with which the user comes into contact orproximity. Many types of sensors do not have fixed applications and canbe used in a variety of applications. One area of HCI research exploresusing traditional sensor technology in new and creative ways. Forexample, while a magnetometer is typically used as a sensor for acompass, it can also be used to sense human gestures.

Therefore, it would be desirable to have a sensor that can be used tomeasure a variety of human actions and activity, such as proximity ortouch, deformation and manipulation of objects and other actions thatcan be used to sense the presence and intention of a human being andthat can be used as part of a user interface for a computer system.

SUMMARY

One embodiment disclosed herein is a system for sensing interaction. Thesystem includes a signal generator producing a frequency-swept signal inan object. The system includes an impedance measurement componentcoupled to the object and configured to identify a change in animpedance parameter of the frequency-swept signal as an external bodyinteracts with the object. The system further includes an interactionsignal generator indicating a characteristic of an interaction betweenthe object and the external body based upon the change in the impedanceparameter.

Another embodiment disclosed herein is a method for sensing a body'sinteraction with an object. The method includes generating afrequency-swept signal within the object. The method includesidentifying a change in an impedance parameter of the frequency-sweptsignal as the body interacts with the object and generating aninteraction signal indicating a characteristic of an interaction betweenthe body and the object based upon the change in the impedanceparameter.

Another embodiment disclosed herein is an interactive object. Theinteractive object includes a body having a characteristic reactance anda first interface configured to couple the characteristic reactance toan external scanning impedance monitoring device. The interactive objectalso includes a second interface configured to couple to a reactancealtering element, whereby the characteristic impedance coupled to thescanning impedance monitoring device is distinguishably altered when thesecond interface is coupled to a reactance altering element.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingfigures. The components within the figures are not necessarily to scale,emphasis instead being placed upon clearly illustrating the principlesof the invention. Moreover, in the figures, like reference numeralsdesignate corresponding parts throughout the different views.

FIG. 1 is a block diagram illustrating an embodiment of a system forsensing human activity by monitoring impedance.

FIG. 2A is a graphical view illustrating an example of a measurablechange in the resonant frequency of an object due to human interaction.

FIG. 2B is a graphical view illustrating an alternative measurableparameter of the object of FIG. 1.

FIG. 3 is a graphical illustration showing the effect of a biasinginductor on the capacitance and resonant frequency of an object.

FIG. 4A is a graphical illustration showing an exemplary plot of thestatic resonant frequency of an object.

FIG. 4B is a graphical illustration showing an exemplary plot of theresonant frequency of the object of FIG. 4A after human interaction.

FIG. 5 is a schematic diagram illustrating a first example of a mannerin which the system for sensing human activity by monitoring impedancecan be used.

FIG. 6 is a schematic diagram illustrating a second example of a mannerin which the system for sensing human activity by monitoring impedancecan be used.

FIGS. 7A and 7B are schematic diagrams collectively illustrating anotherexample of a manner in which the system for sensing human activity bymonitoring impedance can be used.

FIGS. 8A and 8B are schematic diagrams collectively illustrating anotherexample of a manner in which the system for sensing human activity bymonitoring impedance can be used.

FIGS. 9A and 9B collectively illustrate a flow diagram describing theoperation of an embodiment of the method for sensing human activity bymonitoring impedance.

DETAILED DESCRIPTION

The system and method for sensing human activity by monitoring impedanceis based on a physical phenomenon known as impedance. Impedance isgenerally defined as the total opposition a device or circuit offers tothe flow of an alternating current (AC) at a given frequency. For manyobjects, the frequency at which the opposition to the flow ofalternating current drops to its minimum is referred to as the object'sresonant frequency. Resonant frequency is related to the effect of theelectromagnetic resonance of an object. For some objects, the value ofthe impedance is minimal at the object's resonance frequency and forother objects the value of the impedance is maximal at the object'sresonant frequency. Electromagnetic resonance has been widely used fortuning and filtering radio communication circuits, as well as foridentifying and tagging objects. These uses assume that the resonantcharacteristics of the object are known ahead of time, whereby the usermanipulates a specific tag or identification card. However, any systemof conductive objects, including humans, has resonant properties thatcan be described by defined impedance parameters, such as resonantfrequency, or other parameters. For these reasons, the electromagneticresonance, and in particular, resonant frequency, can be used as anindicator for sensing human activity. Assuming that the electricalproperties of the object or system are constant, any changes in theresonant properties of the object or system result from user activity oruser interaction. Therefore, human interaction with the object or systemcan be detected by a) measuring the impedance of the system at variousfrequencies and generating what are referred to as “impedance curves”that are representative of the system's impedance over a range offrequencies, b) computing various resonant properties and other featuresfrom the impedance curves, and c) monitoring changes in the computedresonant properties of the object or system at different frequencies.Resonant properties include the resonant frequency of the object orsystem as well as other resonant properties, such as an amplitude of ameasured signal at the resonant frequency, the profile of the peaks ofthe measured signal, as well as the presence of other peaks on animpedance curve.

Changes in the resonant properties of the object or system arise due todirect or indirect interaction between a user and the object or system.For example, by measuring changes in the resonant frequency of an objectwhen a user interacts with the object, the type and extent of theinteraction can be identified. The remainder of this description willgenerally focus on monitoring changes in the resonant frequency andother related impedance parameters of an object or system to determinethe type of and extent of human interaction with the object or system.As used herein, the terms object and system will be used interchangeablyto refer to an object or system, the impedance, and in an embodiment,the resonant frequency of which is sought to be measured and monitoredto determine human interaction with the object or system.

Any electrical system with capacitive, inductive and resistive elementshas a unique frequency at which an alternating current flowing throughthe system will reach a maximum or a minimum value, i.e., its resonantfrequency. The maximum and minimum values could also take the form oflocal minimum and local maximum values. While many systems correspond toa minimum alternating current value at their resonant frequency, thereare some systems that correspond to a maximum alternating current valueat their resonant frequency. Both instances are contemplated herein,depending on the system. The system can be stimulated by applying aperiodic electrical signal over a range of different frequencies, e.g.by performing a frequency sweep of the system. The amplitude of thealternating current reaches its minimum or maximum at the resonantfrequency of the system, and can therefore be used as an indicator ofthe resonant frequency of the system.

Any interaction that affects the reactive properties of the system (i.e.capacitance or inductance) will change the impedance characteristics,and in an embodiment, the resonant frequency of the system. Assuming theelectrical properties of the system remain constant, any changes in theresonant frequency will occur due to human activity or interaction withthe system. Thus, it is possible to infer human interaction with thesystem by tracking changes in the resonant frequency of the system.

The resonant frequency of a circuit that includes capacitive, inductiveand resistive properties can be generally described by Equation 1.

$\begin{matrix}{f_{0} = \frac{1}{2\pi\sqrt{L \cdot C}}} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

where L is the inductance in C is the capacitance of the system. Theresonant frequency of the system changes only when the system'sinductance and capacitance are affected.

Capacitive interactions change the capacitive properties of the system.For example, a user touching a conductive object, such as a metalbracelet worn on a user's wrist, forms a capacitive link to ground,increasing capacitance and decreasing the resonant frequency of thebracelet. Another example of capacitive interaction is the physicalreconfiguration of the object such as opening or closing a drawer in ametal cabinet. Such reconfiguration leads to changes in systemcapacitance and changes in the resonant frequency.

Inductive interactions change the inductive properties of the system.For example, stretching a metal spring will change its inductance, asthe inductance depends on the distance between the turns of the spring.Changing the inductance changes the resonant frequency of the system.Accordingly, a sensor configured to determine the resonant frequency ofan object or system should be sensitive to changes in the capacitanceand inductance of the object or system.

FIG. 1 is a block diagram illustrating an embodiment of a system forsensing human activity by monitoring resonant frequency. The sensingsystem 100 is coupled to an object 110 over connection 102. In anembodiment, the connection 102 can be a single wire. An electrode 105can be attached to the object 110, or can be attached to a human 118,depending on the application.

The object 110 can be any conductive object or system that haselectromagnetic resonant properties and, in an embodiment, a resonantfrequency characterized by an inductance (Lo) 112 and a capacitance (Co)114. The inductance (Lo) 112 and the capacitance (Co) 114 can be knownor unknown. The inductance (Lo) and the capacitance (Co) correspond tothe inductance, L, and the capacitance, C, in Equation 1. To illustratehuman interaction, a human 118 touches the object 110, in which thetouch illustrates a capacitive contact between the human 118 and theobject 110. The capacitance, Ct, 116 illustrates that the touch causes achange in the overall capacitive reactance of the object 110. Aparticular configuration of inductive and capacitive elements in theobject 110 are provided as an example. In general the exactconfiguration may not be known and can be arbitrary and complex.However, the operation of the systems and methods described herein arenot dependent on knowledge of the exact configuration of the inductiveand capacitive elements in the object 110.

The sensing system 100 comprises a signal generator 120, an envelopedetector 122, a microprocessor 124, an analog to digital converter 126,and a memory 128, coupled over a system bus 154. The system bus 154 canbe any communications bus that allows interoperability and communicationbetween and among the connected elements. The microprocessor 124 can beany general purpose or special-purpose processor that can execute thefunctions described herein. The memory 128 can be any type of static ordynamic memory, volatile or non-volatile memory, and can, in anembodiment, be used to store software related to the operation of thesystems and methods described herein. The memory 128 can be either orboth of local memory and/or memory located on other computing devicesand that is accessible using various data transmission technologies,such as wired or wireless connection links. The memory is also used tostore the results provided by the sensing system 100.

The signal generator 120 generates a time varying signal f(t), which isprovided over connection 132. In an embodiment, the signal provided overconnection 132 is a 1 KHz to 3.5 MHz, 10V peak-to-peak, sinusoidalfrequency sweep, which is provided to a resistor 134. The resistor, Rs,134 has a relatively small value and converts the alternating current onconnection 132 to an alternating voltage on connection 136. Thealternating voltage on connection 136 is provided through a node 138 toa first switch 142 and to a second switch 146. The switches 142 and 146can be controlled manually, by the microprocessor 124 or by anycircuitry that can be specific to the embodiments described. The firstswitch 142 is connected to a biasing inductor, Ls, 144, and the secondswitch 146 is connected to a biasing capacitor, Cs, 148. The switches142 and 146 can be selectively opened and closed by the microprocessor124, or by other logic or circuitry. For most objects, the capacitance,Co, 114 and the inductance, Lo, 112 are very small, resulting in a veryhigh resonant frequency.

Both capacitive and inductive interactions with the object 110 affectthe form of the impedance curve, as well as the width of local or globalpeaks in the impedance curve corresponding to resonant frequency i.e.,it's Q-factor, with a resultant change in the resonant frequency of theobject 110, or a change in other parameters To infer human interactionwith the object 110 from changes in a measurable parameter, acorrespondence between human interaction and the affected parametershould be established. Therefore, it could be preferable in someapplications to block the effect of either capacitive or inductiveinteractions. Doing so ensures that changes in the resonant frequency,or Q-factor, are the result of changes in one, but not both types ofinteractions. For example, if it is desirable to measure the stretchingof twisted wire, i.e. an inductive interaction, it would be desirable toremove the influence of the user touching the wire, which is acapacitive interaction and which would also affect the measurement ofthe resonant frequency.

Blocking the influence of inductive interactions can be accomplished byadding the biasing inductor, Ls, 144, and blocking the influence ofcapacitive interactions can be accomplished by adding the biasingcapacitor, Cs, 148. In addition to blocking the influence of inductiveand capacitive interactions, selectively introducing the biasinginductor, Ls, 144 and the biasing capacitor, Cs, 148 between theconnection 136 and the connection 102 also shifts the resonant frequencyof the entire system including the sensing system 100 and object 110into a lower range that is more easily measured than a very highresonant frequency. For example, if it is desired to track capacitancechanges in the system 110, a large value for the biasing inductor, Ls,144 not only blocks the influence of inductive changes in the object110, but also shifts the resonant frequency into a lower, more easilymeasurable range. Similarly, if it is desirable to track inductivechanges in the object 110, a large biasing capacitor, Cs, 148 isswitched into the system, thus blocking the influence of capacitivechanges in the object 110 and shifting the resonant frequency into alower, more easily measurable range. Generally, either the biasinginductor, Ls, 144 or the biasing capacitor, Cs, 148 will be connected tonode 138 at a given time. The biasing inductor, Ls, 144 and the biasingcapacitor, Cs, 148 can be referred to as reactance altering elementsbecause they influence the AC voltage on node 138.

The large biasing inductor, Ls, 144 blocks inductive effects imparted tothe object 110, thus enabling the measurement of small changes incapacitance. A large biasing capacitor, Cs, 148, blocks capacitiveeffects, thus enabling the measurement of small changes in inductance ofthe object 110.

In an embodiment, the alternating voltage at node 138 characterizes theresonant frequency of the object 110, including the effect imparted bythe biasing inductor, Ls, 144 or the biasing capacitor, Cs, 148. Thealternating voltage at node 138 is provided to an envelope detector 122.The envelope detector 122 generates a time varying DC signal thatdefines the amplitude of the alternating voltage at node 138. The signalon connection 152 represents a signal returned from the object 110. Thetime varying DC signal is provided to the analog to digital converter(ADC) 126. The analog to digital converter 126 processes the timevarying DC signal provided by the envelope detector 122 to determine alocal minimum, a local maximum, or other attribute of the measuredsignal. In an embodiment, the local minimum of the time varying DCsignal corresponds to the resonant frequency, f₀, of the object 110. Thesignal representing the resonant frequency, f₀, is provided overconnection 162 to systems external to the sensing system 100. In anembodiment, the signal, f₀, is provided to an interface 170. Theinterface 170 can be any interface that can use the information aboutthe resonant frequency of the object 110. For example, the interface 170can be a user interface that provides an input/output function to acomputing device, a portable communication device, an interactive toy, asensing system associated with an attraction at an amusement park, orany other computer-based interface. The output of the interface onconnection 172 is shown as being provided to another system to signifythat the output of the sensing system 100 can be used by a number ofdifferent systems in a number of different configurations.

The ability to accurately measure the resonant frequency of an object110 with very small capacitance and inductance allows the resonantfrequency of the object to be identified and tagged, thereby providingthe ability to recognize the object 110 based on its resonant frequency.For example, the resonant frequency of the object 110 can be measuredand stored in the memory 128 so that at a later time, the resonantfrequency can be used to identify that object 110.

FIG. 2A is a graphical illustration 200 of an example of a measurablechange in the resonant frequency of an object due to human interaction.The vertical axis 202 represents amplitude of a measured signal and thehorizontal axis 204 represents frequency. A first resonant frequencytrace 206 illustrates a measured signal that has a first resonantfrequency f₀. A second resonant frequency trace 208 illustrates ameasured signal that has a second resonant frequency, referred to as fl.In an embodiment, the resonant frequency, f₀, can be the static resonantfrequency of the object 110. The second resonant frequency, f₁,represents the resonant frequency of the object 110 while being touchedby a human being 118. As shown in FIG. 2A, the change in the resonantfrequency, referred to as Δf, 210, shows the effect of a human beinginteracting with the object 110 by touching the object 110. For example,if the object 110 is a wristwatch bracelet that is connected to thesensing system 100 with an electrode 105 over connection 102, the effectof a human being 118 touching the object 110 results in a change in theresonant frequency of the object by an amount shown in FIG. 2A as Δf.The ability of the sensing system 100 to measure this change in resonantfrequency allows the sensing system 100 to be used as a user interface,or as part of a user interface that can communicate human interactionwith the object 110 to other computing devices and computing systems.

FIG. 2B is a graphical view illustrating an alternative measurableparameter of the object of FIG. 1 that can be measured by the sensingsystem 100. The vertical axis 222 represents amplitude and thehorizontal axis 224 represents frequency. A first resonant frequencytrace 226 illustrates a measured signal that has a first resonantfrequency f₀. A second resonant frequency trace 228 illustrates ameasured signal that has a second resonant frequency, referred to as f₁.In this example, the first resonant frequency f₀ is substantiallysimilar to the second resonant frequency f₁. In an embodiment, theresonant frequency, f₀, can be the static resonant frequency of theobject 110. The second resonant frequency, f₁, represents the resonantfrequency of the object 110 while being touched by a human being 118.

In FIG. 2B, a change in the amplitude from the first resonant frequencytrace 226 to the second resonant frequency trace 228, referred to asΔamplitude 230 results from human interaction with the object 110. Inthis embodiment, amplitude is the defined impedance parameter and theamplitude difference, Δamplitude 230, can be measured by the ADC 126 andused to signify human interaction with the object 110. Further, acombination of frequency and amplitude can be measured and used tosignify human interaction with the object 110.

FIG. 3 is a graphical illustration 300 showing the effect of a biasinginductor on the capacitance and resonant frequency of an object. Thevertical axis 302 represents resonant frequency in kHz and thehorizontal axis 304 represents capacitance in pF. The traces 312, 314,316 and 318 respectively show the effect of biasing inductance, Ls, 144(FIG. 1) values of 10 μH, 22 μH, 100 μH and 220 μH. As inductanceincreases, the resonant frequency becomes more sensitive to smallvariations in capacitance in lower range of values as the resonantfrequency drops. Therefore, small variations in capacitance can bemeasured at very small values while remaining in a lower range ofresonant frequencies. At the same time it can be observed that as thevalue of inductance increases, the system becomes less sensitive tosmall changes in total inductance. Therefore, by including a largebiasing inductor, the effect and influence of inductance can beeffectively blocked. Blocking the inductance will ensure that changes inthe resonant frequency can be measured by small capacitive interactiononly. Alternatively, a large biasing capacitor can be used to block theinfluence of capacitance changes and allow the measurement of resonantfrequency as a result of small changes in inductance.

FIG. 4A is a graphical illustration 400 showing an exemplary plot of thestatic impedance of an object. The vertical axis 402 representsamplitude and the horizontal axis 404 represents frequency. The trace406 illustrates a plot of the static impedance curve of the object 110.The term “static” impedance refers to the impedance of the object 110with no human interaction. The trace 406 shows the static impedancecurve of the object 110 over a range of different frequencies. Theresonant frequency, fo, is illustrated at 408. The resonant frequency408 can be stored in the memory 128 and can be associated with theobject 110. Associating the resonant frequency 408 with the object 110allows the identity of the object 110 to be saved and used at asubsequent time to identify the object 110.

FIG. 4B is a graphical illustration 420 showing an exemplary plot of theimpedance of the object of FIG. 4B during human interaction. Thevertical axis 422 represents amplitude and the horizontal axis 424represents frequency. The trace 426 illustrates a plot of the impedancecurve of the object 110 during human interaction. The trace 426 showsthe impedance curve of the object 110 over a spectrum of differentfrequencies and reflects changes in the static impedance curve of FIG.4A shown by trace 406. The change in the impedance curve shown in trace426 reflects changes in one or more impedance parameters of the object110 resulting from human interaction. These changes result in a changein, for example, the resonant frequency, which changes from a value f₀in FIG. 4A to a value of f₁ in FIG. 4B. Changes in other impedanceparameters, such as amplitude, a combination of resonant frequency andamplitude, or other impedance parameters can also be monitored forchange which can signify human interaction with the object 110. Otherfeatures of the impedance curve, such as differences in the amplitude,shape and width of a peak 412 (FIG. 4A) and a corresponding peak 432(FIG. 4B), can be monitored for change, which can also signify humaninteraction.

As an example of human interaction with the object 110, when a usertouches the object 110 with their finger, the user's finger creates avariable capacitance with the object. The capacitance can vary with theamount of pressure exerted by the user's finger on the object. As theuser presses harder, the skin stretches and increases the area of touch,thereby increasing the capacitance, and thereby altering the trace 426.The resonant frequency, is the resonant frequency of the object 110 inresponse to the human interaction and is illustrated at 428. Thedifference in resonant frequency, Δf, 430, reflects the difference inresonant frequency between f₀ and f₁, and is indicative of the humaninteraction with the object 110. The value of f₀, f₁ and Δf can bestored in the memory 128 and used to identify the object 110 and thetype of interaction with the object 110. In addition to the frequency,other parameters, such as, for example, the amplitude of the trace at aparticular frequency can also be monitored for change that can signifyhuman interaction. For example, a point, P1, on the trace 406 in FIG. 4Amight occur at an amplitude, A₀. The point P1 may exhibit a change inamplitude, shown as A₁ in FIG. 4B, to signify human interaction, andfurther, to signify a degree of human interaction.

FIG. 5 is a schematic diagram illustrating a first example of a mannerin which the system for sensing human activity by monitoring impedancecan be used. The electrode 105 is attached to the user's body 118, suchas to a finger or wrist. The sensing system 100 records changes of theparameters describing the impedance curve (FIGS. 4A and 4B) as the usertouches various objects in the environment or changes their relation tothe environment. In FIG. 5, the user 118 is touching their own body,such as another arm, fingers or a cheek, or in this example, their hand502. The change in the measured impedance parameter or parametersdepends on, for example, the extent to which the user 118 touches theirown body, e.g. the area of contact and the force of contact. Themeasured impedance parameters can determine, for example, whether theuser touches them self with one finger, with two fingers or with threefingers. The measured impedance parameters can also be used to determinehow much pressure the user applies. The measured impedance parameterscan be then mapped to correspond to various interaction actions. Forexample, tapping ones hand with one finger could start playback of adigital music player, while tapping ones hand with two fingers couldstop playback of the digital music player. Other media devices, gamedevices, communication devices, appliances, etc., and their relatedfunctionality can be controlled in similar manner.

In another example, one or more of the parameters of a music synthesisdevice could be controlled by the user squeezing their own arm, wheresqueezing the arm stronger, for example, could increase the pitch of thesound. In another example, an external system can be controlled byclapping, where the sensing system 100 can recognize the extent to whichthe clapping hand is touching the other hand, e.g. if it is touchingonly with the tips of the finger or with the entire palm. This measuredimpedance characteristic can be then applied to control the device.

In another example the user 118 can distinguish which parts of their ownbody the user is touching, either by equipping the body with additionalelectrodes or by recognizing that different body parts have differentelectrical properties.

In other examples, the user may raise one or both feet from the ground.The change in measured impedance parameters could describe how much theuser 118 raises their feet from the ground, as well as if the userraises one foot or both feet. The measured impedance parameters can beused to measure user state and can be saved to memory 128 (FIG. 1) andmapped to control at least some of the parameters of the interaction.For example, comparing the measured impedance parameters can determinewhether the user is touching the ground with his feet, which allows themeasurement of the number of steps the user has taken and otherproperties of locomotion. For example, comparing the measured impedanceparameters can distinguish between running and walking.

The system and method for sensing human activity by monitoring impedancecan also be used to distinguish different objects that the user may betouching or with which the user may be in proximity. Different objectscould affect parameters of the impedance curves differently when theuser touches them. Based on the measured impedance parameters, it ispossible to distinguish how and to what extent the user is touching theobject, e.g. how hard the user is touching the object, how many fingersare touching the object and so on. This is possible because the largerthe area of contact with the object, the more pronounced will be thechange in the measured impedance parameters. The sensing system 100 candistinguish between the objects that the user is touching as follows.For one or more objects, when the user touches an object the sensingsystem 100 records the measured impedance parameters of the impedancecurve and stores the measured impedance parameters in the local memory128 (FIG. 1). Subsequently, if the user 118 touches the same object, thesensing system 100 compares the subsequently measured impedanceparameters with those stored in the memory 128 and if a match is found,identifies the object 110. There are a number of ways this can beaccomplished. The object can be distinguished without anyinstrumentation, by measuring impedance parameters of the impedancecurve (426, FIG. 4B). Alternatively, the object 110 can be instrumentedwith additional passive components (e.g. capacitors and inductors) tocreate a unique “signature” that would allow the sensing system 100 todistinguish which object the user is touching. If the object consists ofdifferent parts, such as individual drawers, doors, legs, etc, thesensing system 100 can distinguish which part the user is touching. Inanother example, the other object can be a person. For example, shakinghands can result in a unique impedance curve and have a unique measuredimpedance parameter. Further, the measured impedance parameter canreflect differences depending on how many people are touching eachother. Therefore, the sensing system 100 can distinguish when severalpeople are joining hands and form a larger configuration of people.

It is also possible to track an object inside of the user's body. Themeasured impedance parameter of the impedance curve changes when theuser is changing the properties of the body. For example, if anelectrode 105 is attached to a user's cheek, the sensing system 100 cantrack when the user 118 moves water inside of their mouth.

FIG. 6 is a schematic diagram illustrating a second example of a mannerin which the system for sensing human activity by monitoring impedancecan be used. In the example shown in FIG. 6, the user 118 does not wearthe electrode 105 on their body, but instead holds a mobile device 610in their hand 602. In this example, the mobile device is a mobile phone.The mobile device 610 has an electrode 105 embedded in its case. Anadvantage of this configuration is that the user does not have to wearanything. The interaction starts naturally when the user 118 picks upthe mobile device 610. Another advantage is that the effects of theinteraction are defined and encapsulated by the mobile device 610, i.e.a different device would have different effects. For example if the user118 holds a mobile device 610 and touches their holding hand 602 withanother hand 615, then a call can be put on hold. However, if the deviceis a gaming device, performing the same actions could result in a gamerelated action, such as shooting or flying. Other applications can alsobe designed.

FIGS. 7A and 7B are schematic diagrams collectively illustrating anotherexample of a manner in which the system for sensing human activity bymonitoring impedance can be used. The sensing system 100 can recognizeproperties of touch when a user 118 is touching the electrode 105. Forexample if the object is an interactive toy 705, the sensing system 100can recognize the user 118 touching the object as well as how stronglythe user is touching the object, such as using a single finger in FIG.7A and using two fingers in FIG. 7B, and then cause an interface (170,FIG. 1) associated with the sensing system 100 to react in a mannerappropriate to the touch.

The electrode 105 can be attached to a non-conductive object, which, inan embodiment, can be used as a handle for the electrode 105. Forexample the electrode 105 can be attached to the end of the wooden stickthat is used like a magic wand. The handle of the non-conductive objecttherefore can be manipulated by the user in a way that the internalstate of the user does not affect the sensing system 100. Advantages ofthis arrangement include there being a much clearer and directconnection between the electrode 105 and the objects in the environmentsthat the user is interacting with, as opposed to the case where theelectrode is attached to the user's hand. Furthermore, the internalstate of the user 118 would not affect the measured signal because theuser 118 and the sensing system 100 are separated.

The sensor 105 can also be attached to a conductive object located inthe environment. The sensing system 100 recognizes individuals who aretouching the object by analyzing the measured impedance parameters thatcan be associated with a particular individual. The sensing system 100can distinguish between people of different sizes, e.g. large body andsmall body. The sensing system 100 can distinguish between children andadults. For example an attraction in an amusement park can behavedifferently depending on whether a child or an adult interacts with theattraction.

The sensing system 100 also can distinguish between humans andnon-humans, or between humans and multiple humans. For example, thesensing system 100 can be used to accurately track the presence ofhumans in ride vehicles in an amusement park.

When implemented as a stylus used as an input device, the stylus can beinstrumented with one or more electrodes and/or sensing systems andchange the properties of an interface depending on how the user isinteracting with the stylus. For example, a light touch on the styluscould create a thin line and strong touch on the stylus could create athick line.

In another example, a computer input device can track the proximity of atouching finger and then clearly distinguish between touch and proximityof the user to the object.

The object can become interactive in an adhoc manner, i.e. an object 110was not interactive before but becomes responsive to user interactionafter the sensing system 100 is attached to it. For example, arefrigerator could become interactive when the sensing system 100 andelectrode 105 are attached to it.

In another example, an electrode 105 can be placed into water or otherconductive liquid and then one or more parameters of the liquid can bemeasured by monitoring a change in the measured impedance parameter. Thesensing system 100 system could also respond depending on how much ofthe object 110 is placed into the water, e.g. a partially submergedobject would produce a different reaction from completely submergedobject. An amount of liquid flowing through an object, such as a pipe,can also be measured. Interaction with running liquid can also bemeasured.

Changes in the internal state of the object 110 can also be measured.These changes can be caused by the user 118 as they interact with theobject 110, environment or internal changes in the object 110.

In another example, the electrode 105 can be attached to an object 110and the object 110 can “sense” changes in its configuration. Forexample, a refrigerator can recognize when the door is open or closed,or a cabinet can be instrumented to recognize when a specific drawer isopen.

In another example, the sensing system 100 can measure the wear of anobject 110 as the user 118 interacts with it. For example, the sensingsystem 100 can be attached to the graphite core of a pencil and aconductive plane can be placed underneath the paper. The sensing system100 can measure the exact area of touch of the pencil tip on the paperand as the user sketches and the tip of the pencil wears, the area ofpen touching paper can be continually tracked. This information can bemapped into the thickness and other properties of lines that are beingdrawn on the paper.

The sensing system 100 can measure the growth of an object 110 such as aplant. The sensing system 100 can also measure how the configuration ofthe plant changes with time or how the internal state of the plantchanges with time.

FIGS. 8A and 8B are schematic diagrams collectively illustrating anotherexample of a manner in which the system for sensing human activity bymonitoring impedance can be used. The electrode 105 can be attached to astretchable object 810 and can be used to measure the amount that theobject 810 stretches. Stretching is an inductive interaction. In thisexample, it is desirable to estimate the changes in the inductiveproperties of the object 810. In an example, the object 810 is aflexible coil and the sensing system 100 can measure how far the user118 is stretching the flexible coil. As an example, the flexible coilcan be a conductive thread 811 that is woven into fabric 807 of agarment worn by the user 118. As the fabric 807 stretches, theconductive thread 811 also stretches. The amount that the conductivethread 811 stretches can be indicated by analyzing the measuredinductive parameters that indicate the extent of stretching the fabric807 and the conductive thread 811. In this example, the sensing system100 can be used to measure interaction with plush toys and interactiveclothing. For example, the conductive thread 811 can be woven into thefabric 807 and as the user 118 dances, moves, plays games, etc.,environmental surroundings, such as music and lighting, can becontrolled by the motion and stretching of the garment, via theinterface 170 (FIG. 1).

In another example, the coil of conductive thread 811 can be wrappedaround the user's finger or leg or other body part. As the user 118bends their finger (or leg) the configuration of the coil of conductivethread 811 changes and results in a change in the measured impedanceparameter. In this manner, the amount of movement can be measured, thusallowing the development of devices such as, for example, a data gloveand motion capture suit, e.g. an instrumented garment that can recognizeand record changes in user posture in time, and communicate suchinformation to other systems.

FIGS. 9A and 9B collectively illustrate a flow diagram 900 describingthe operation of an embodiment of the method for sensing human activityby monitoring impedance. The blocks in the flow chart of FIGS. 9A and 9Bcan be performed in or out of the order shown. In addition, at leastsome of the blocks can be performed in parallel.

In block 902, the signal generator (120, FIG. 1) generates a timevarying signal f(t). In an embodiment, the time varying signal f(t) is a1 KHz to 3.5 MHz, 10V peak-to-peak, sinusoidal frequency sweep. Howeverother ranges of frequencies and signal amplitudes can be used.

In block 904, a biasing inductor shifts the object's resonant frequencyto a lower frequency range and blocks inductive effects, therebyfacilitating the measurement of small changes in capacitance.

Alternative to block 904, in block 906, a biasing capacitor shifts theobject's resonant frequency to a lower frequency range and blockscapacitive effects, thereby facilitating the measurement of smallchanges in inductance. In block 908, the time varying signal f(t) isconverted to a voltage.

In block 912, the time varying voltage signal f(t) is converted to atime varying DC signal. The time varying DC signal defines thealternating voltage at node 138 (FIG. 1).

In block 914, the time varying DC signal is processed to compute one ormore impedance parameters of the measured signal. In an embodiment, alocal minimum, or other attribute of the signal, is located. In anembodiment, the local minimum of the time varying DC signal correspondsto the resonant frequency, f₀, of the object 110. However, otherimpedance parameters of the signal can also be located that define otherelectromagnetic resonant attributes.

In block 916, the impedance parameter of the object 110 is saved to thememory 128 (FIG. 1). In an embodiment, the resonant frequency, f₀, ofthe object 110, or another impedance parameter of the signal, is savedto the memory 128 (FIG. 1). For example, the amplitude of the signaltrace can be saved to memory 128 (FIG. 1) and used as an indicator ofhuman interaction. The memory 128 can be either or both of local memoryand/or memory located on other computing devices and that is accessibleusing various data transmission technologies, such as wired or wirelessconnection links. The impedance parameter can also be compared to otherimpedance parameters that have previously been saved to the memory 128(FIG. 1) to identify the current impedance parameter.

In block 918, it is determined whether the process is to continue. Ifthe process is to continue, in block 922 it is determined whether thereis more than one resonant frequency measurement in memory 128 (FIG. 1).If the process is to continue and there is only one resonant frequencymeasurement in memory 128 (FIG. 1), the process proceeds to block 902.If the process is to continue and there is more that one resonantfrequency, or other parameter of the signal, measurement in memory 128(FIG. 1), the process proceeds to block 924. In some applications it maybe desirable to measure and record a single resonant frequency of anobject. In such an application, the process ends after block 918.

In block 924, a first impedance parameter trace and a second impedanceparameter trace are collected. In block 926, an attribute of the firstimpedance parameter trace is compared with a corresponding attribute ofthe second impedance parameter trace. As an example, the resonantfrequency, f₀, of the first impedance parameter trace is compared with aresonant frequency, f₁, of the second impedance parameter trace.Alternatively, other attributes of the respective impedance parametertraces can be compared.

In block 928, it is determined whether the first resonant frequency, f₀,and the second resonant frequency, f₁ are substantially equal. If thefirst resonant frequency, f₀, and the second resonant frequency, f₁, aresubstantially unequal, then the process proceeds to block 932, where thechange in resonant frequency is noted and signifies human interactionwith the object. In alternative embodiments, other impedance parametersof the measured signal can be compared to determine whether there hasbeen human interaction.

If it is determined in block 928 that the first resonant frequency, f₀,and the second resonant frequency, f₁, are substantially equal, then itis assumed that there is no human interaction with the object 110 andthe process proceeds to block 934, where it is determined whether theprocess is to continue. If the process is to continue, the processreturns to block 902 (FIG. 9A).

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible that are within the scopeof the invention.

What is claimed is:
 1. A system for sensing interaction, comprising: asignal generator producing a frequency-swept signal in an object; animpedance measurement component coupled to the object and configured toidentify a change in an impedance parameter of the frequency-sweptsignal as an external body interacts with the object; a switchingelement selectively coupling a reactive component to an electrical pathpropagating the frequency-swept signal, wherein the reactive componentis selectively coupled to both the signal generator and the impedancemeasurement component via the switching element, wherein the reactivecomponent is operable to shift a resonant frequency associated with theobject based on a state of the switching element; and an interactionsignal generator indicating a characteristic of an interaction betweenthe object and the external body based upon the change in the impedanceparameter.
 2. The system of claim 1 wherein the frequency-swept signalcomprises a time-varying frequency component that varies within a rangeof substantially 1 KHz to 3.5 MHz.
 3. The system of claim 1 wherein thefrequency-swept signal is a periodic electrical signal.
 4. The system ofclaim 1 wherein the characteristic of the interaction indicated by theinteraction signal generator comprises one of: a location of the objectcontacted by the external body, a pressure of the contact between theobject and the external body, and a size of an area of contact betweenthe object and the external body.
 5. The system of claim 1 wherein theimpedance measurement component is coupled to the object with a singleelectrode.
 6. The system of claim 1 wherein the impedance measurementcomponent identifies the change in the impedance parameter by comparinga first multi-frequency impedance curve of the object measured when theobject and the external body are not interacting to a secondmulti-frequency impedance curve measured when the object and theexternal body are interacting.
 7. The system of claim 1 wherein theimpedance parameter is at least one of: a resonant frequency of thefrequency-swept signal, amplitude of the frequency-swept signal at aparticular frequency, a difference between amplitudes at respectivefrequencies of the frequency-swept signal, and a shape of an impedancecurve generated by the frequency-swept signal.
 8. The system of claim 1,wherein, based on the state of the switching element, the reactivecomponent is operable to block an influence of a reactive effectimparted to the object thereby improving an ability to identify thechange in the impedance parameter.
 9. A method for sensing a body'sinteraction with an object, comprising: generating a frequency-sweptsignal within the object using a signal generator; selectively couplinga reactive component to an electrical path of the frequency-swept signalusing a switching element; identifying a change in an impedanceparameter of the frequency-swept signal as the body interacts with theobject using an impedance measurement component, wherein the reactivecomponent is selectively coupled to both the signal generator and theimpedance measurement component via the switching element, wherein thereactive component is operable to shift a resonant frequency associatedwith the object based on a state of the switching element; andgenerating an interaction signal indicating a characteristic of aninteraction between the body and the object based upon the change in theimpedance parameter.
 10. The method of claim 9, wherein the act ofgenerating a frequency-swept signal comprises generating multiplefrequencies over a period of time in the range of substantially 1 KHz to3.5 MHz.
 11. The method of claim 9 wherein the act of generating thefrequency-swept signal comprises applying an electrical signalperiodically to the object.
 12. The method of claim 9 wherein thecharacteristic of the interaction indicated by the interaction signalcomprises one of: a location of the object contacted by the body, apressure of the contact between the object and the body, and a size ofan area of contact between the object and the body.
 13. The system ofclaim 9 wherein the act of generating an interaction signal comprisesmeasuring the impedance parameter of the frequency-swept signal using asingle conductor.
 14. The method of claim 9, wherein the act ofidentifying the change in an impedance parameter comprises comparing afirst multi-frequency impedance curve of the object measured when theobject and the body are not interacting to a second multi-frequencyimpedance curve measured when the object and the body are interacting.15. The method of claim 9, wherein the impedance parameter is at leastone of: a resonant frequency of the frequency-swept signal, amplitude ofthe frequency-swept signal at a particular frequency, a differencebetween amplitudes at respective frequencies of the frequency-sweptsignal, and a shape of an impedance curve generated by thefrequency-swept signal.
 16. An interactive object comprising: a bodyhaving a characteristic reactance; a first interface configured tocouple the characteristic reactance to an external scanning impedancemonitoring device, wherein the external scanning impedance monitoringdevice comprises a switching element, wherein the switching elementselectively couples a reactive component to an electrical pathpropagating a frequency-swept signal, and wherein the reactive componentis selectively coupled, via the switching element, to both a signalgenerator that generates the frequency-swept signal and an impedancemeasurement component in the external scanning impedance monitoringdevice, wherein the reactive component is operable to shift a resonantfrequency associated with the interactive object based on a state of theswitching element; and a second interface configured to couple to areactance altering element, whereby the characteristic reactance coupledto the scanning impedance monitoring device is distinguishably alteredwhen the second interface is coupled to the reactance altering element.17. The interactive object of claim 16, wherein the first interface isan electrode configured to permit an electrical signal to flow betweenthe interactive object and the external scanning impedance monitoringdevice, wherein an impedance parameter of the electrical signal isaffected when the second interface is coupled to the reactance alteringelement.